The present invention relates to localized and global control of relatively large surfaces. More particularly the invention relates to the use of electrostatic actuators and pneumatic action to control the shape of a flexible surface. Specifically the invention relates to a low-weight structure useful in controlling the profile of a surface in large area systems.
Activation in two or three dimensional arrays of actuators, particularly where the actuators affect a surface shape over a quasi-continuum, have not been developed to date, even though localized and global shape control of relatively large surfaces would offer significant advantage in various technologies. Examples of these technologies where a significant need exists are, among others, micro adaptive flow control, flight control in micro UAV, acoustics, and drag control.
In order to accomplish the yet to be developed control of surfaces, an actuation principle that allows the actuation of large surfaces with out-of-plane forces is desirable. If there is to be adequate control of small flying objects, simple, light, low power actuators are mandatory. Various actuation devices which affect a surface are known to have drawbacks which prevent their use broadly and certainly limit their use in the various needs described above.
Electromagnetic actuation requires heavy magnetic materials and relatively large currents, and the construction of such devices is not compact enough to be suitable for actuation of large surfaces. Clearly, for flight applications this method is excluded because of poor power/weight performance.
Electrothermally induced actuation is structurally suited for activator arrays, but also has the drawbacks of high power requirements, low speed of response and, in many cases dependence on environmental temperatures. Similarly, piezoelectric actuation, while structurally fitted for actuator arrays and uses low power with adequate or high speed, does not possess the displacements needed and are, in fact, so low as to not be useful for the above considered applications. Piezoelectric materials with increased performance have been proposed, but are both very expensive and heavier than would be acceptable.
In some systems adequate control can be achieved by the use of pneumatic components in the actuation process. In those systems the diaphragms are required to hold a gas inside, requiring adequate thickness to retain the gas, thus leading to heavier films. It would be of particular advantage if a surface shape could be controlled by a device having an array of actuated surfaces which are mechanically controlled, rather than pneumatically actuated, so that thinner and lighter outer surfaces such as membranes could be employed.
In some instances it has been found that the use of the pneumatic component of an electrostatic/pneumatic actuator require relatively thick diaphragm walls, which of course add weight to the device as well. It would be of a significant advantage if a design could be provided which eliminates the need for the diaphragm to hold gas inside.
When combined in an array having a relatively large surface area, it is desirable to have as smooth a surface as possible, for possible use as reflector and antenna applications. This objective would be an advantage in the art if it were to be possible.
It would be of great advantage to the art if a low weight, low power, high performance actuator could be developed which would permit localized and global shape control of relatively large surfaces.
It would be another great advance in the art if actuator arrays could be designed which would permit construction of large two and three dimensional arrays useful in a wide range of applications in flow and sound propagation control.
Other advantages will appear hereinafter.
It has now been discovered that the above and other advantages of the present invention may be realized in the following manner. Specifically, the present invention comprises a series of electrostatic actuation devices which are admirable suited for building large two and three dimensional arrays of actuators that can cooperate to achieve the advantages of the present invention
Extremely simple, the actuator construction of the present invention maybe embedded into the functional device for which it is intended, at a minimum of cost and difficulty. Where a moving surface such as an outer skin of an object is desired, the actuator can be fabricated as the skin. Similarly, where a pump is desired, the actuator becomes the walls of the pump chamber. No additional motors, magnets or high weight power sources are needed. Moreover, the materials required for the electrostatic actuation are conductors for the electrodes and insulators to prevent an electrical short in touch-mode electrostatic actuators, and these materials may be deposited in thin layers over low cost plastic substrates produced by extrusion molding or other methods in desired shapes. The plastic substrates are also available in various off-the-shelf configurations.
The device of this invention broadly comprises a rigid, thin plate with suitable patterned electrodes and embedded circuitry, with a relatively flexible cover. Combined with the plates, the cover creates a cavity that can be sealed. By applying suitable voltages, the shape of the flexible cover can be changed, through the combined effect of electrostatic actuation, built-in elastic force and pneumatic action. Pulling down on the cover in certain areas by electrostatic attraction will result in the displacement of a bubble along the surface, controlled by the pattern of the electrodes and the configuration of the device. Both open and closed cavities are contemplated, as are control of the pressure of the fluid inside the cavity and the magnitude of the built-in elastic force.
Of course, the fluid within the cavity can be a gas or a liquid, depending on the final end use of the product containing the invention. For most flight applications, the fluid will be a gas, while a liquid may be used in other cases such as under water or earth-bound operation.
In a second preferred embodiment, the present invention includes a plurality of individual cells, each cell being operably connected to a large surface area such that the individual cells compound together to provide the desired shape of the large area.
In the most preferred embodiment of this invention, a plurality of cells are provided that include (1) a surface having a shape that is to be controlled, such as a membrane, (2) an underlying infrastructure that supports the top surface in an array of adequately spaced posts, and (3) an actuating mechanism that provides individual control of the vertical position of each supporting post, ensuring control of tilt in each of an array of unit cells.